1. Field of the Invention
The present invention relates to a photodiode array and an optical receiver device including the photodiode array. More particularly, the invention relates to a photodiode array in which the size and pitch of photodiodes can be decreased and crosstalk between the photodiodes can be reduced.
2. Description of the Related Art
An example of a photodiode array used for an optical module is shown in FIGS. 9(a) and 9(b) and FIG. 10. The optical module is used for measuring the intensity of light passing through a multi channel optical fiber array or optical waveguide. The photodiode array used for the module includes a semi-insulative semiconductor substrate 10, and an n-type InP layer 11, an InGaAs layer (light receiving layer) 12, and an InP layer (window layer or cap layer) 13 grown in that order on the substrate. In the InGaAs layer 12 and the InP layer 13, p-type areas 14 are selectively formed by the diffusion of Zn. Light receiving areas (i-type areas between p-type areas and n-type areas) are arrayed at a predetermined distance. A p-type electrode 16 is placed above the p-type area 14, and an n-type electrode 15 of each photodiode is placed on the bottom of the common substrate 10.
However, in the photodiode array described above, crosstalk occurs, resulting in a malfunction. The reason for this is that since the individual photodiodes are formed on the common n-type semiconductor substrate, for example, photo carriers generated in photodiodes Ch1 and Ch3 enter the signal of the adjacent photodiode Ch2, resulting in a malfunction in the photodiode Ch2.
In order to reduce crosstalk, a photodiode array disclosed in Japanese Unexamined Patent Application Publication No. 2001-144278, for example, employs a mesa structure in which the individual photodiodes are isolated by etching. In the photodiode array, by employing the mesa structure, carrier diffusion in the transverse direction between the photodiodes is prevented and crosstalk between the adjacent photodiodes is reduced.
However, in the photodiode array described above, since the signal circuits by photo carriers use a common n-type electrode provided on a common n-type substrate, mixing of signals occurs through the common electrode, and therefore it is difficult to suppress crosstalk sufficiently.